Good stuff Jim, so your assumption is that the sensor is simply a static map between voltages?
But then wtf was the vendor talking about when he said “rev sens” (link http://www.audizine.com/forum/showthread.php/645409-B8-5-S4-stock-versus-APR-Stage-1-tune-versus-Chipwerke-piggy-back?p=10659805&viewfull=1#post10659805 ) ??? I’m kind of amazed they want this thing to work when you “punch the gas pedal”…BUT…there is no actual signal measured to indicate throttle position or RPMS :o. Even when 034/Arin@apr were discussing this piggyback (link http://www.audizine.com/forum/showthread.php/553533-ECU-upgrade-is-91-octane-safe-in-Race-mode-(100-octane)?p=8997549&viewfull=1#post8997549), they assumed RPM’s were grabbed from the cam sensors, which is FALSE. Seems like a sketchy proposition at best, couldn’t add a second harness to grab a signal from somewhere else…makes this thing look extremely budget focused.
Now back to Jim’s graph…
Here’s the technical question - if what 034/Arin say is correct, a PID controller is going to sit there and try and achieve the requested boost. Let’s assume for the sake of discussion that it’s a simple controller, possibly with a feed-forward element, and not something more exotic. If any of you have a basic undergrad course in control systems, you’ll know that this is pretty much integrator wind-up city. So now your boost control (bypass valve) is essentially a max transient response to RBF_AV = 0. How does that affect drivability? Well, IF the controller is gain scheduled on throttle pedal or there is sufficient anti-wind up in place, then maybe it’s OK if you feather the pedal back. But that is a big IF, because the engineers were not tuning the controller to deal with these types of set-points. My guess is they tuned their controller to achieve smooth transients, since all the fueling (feedfoward component)/timing/cam phasing will likely have smaller time scales, and will probably rely on smooth boost curves. Maybe the closed-loop elements of the above systems can save the day, but I would be kind of skeptical. I think the engine will run like crap under the right initial conditions, input sequence and environmental conditions. But the sensation of “boost surge” like described in the AZ thread seems very possible, so now your smooth supercharged engine response has some weird laggy turbo feel. Great.
We’ve seen from Revo logs that bypass is opened ever so slightly near redline or when shifting…this would likely not happen with the re-maped MAP signal. Just a thought, not sure Revo’s strategy is close to correct, but would be impossible to enact with this piggyback.
